ssdd - 29-7-2008 at 12:42
So not too long ago I built a voltage multiplier capable of making some impressive discharges: http://scienceunderground.110mb.com/projects/8.php
Now I was wondering what you guys thought would happen if I took some fused silica and placed an inch thick layer of it over a grounded copper plate.
Then to take this and put the arc from the multiplier through this. Would anything interesting happen at all?
Just wondering if this could be a neat way to make synthetic fulgerites.
I am going to give this a try within the week to see first hand.
-ssdd
12AX7 - 29-7-2008 at 13:04
Ewwwwww, so you uploaded six megapixel images, which take several minutes to download even on a reasonable connection, and reduce them all to ~300
pixels across, thereby discarding not only 100 times the information, but also painfully slowing down most any computer viewing this page?!
indigofuzzy - 29-7-2008 at 15:38
Synthetic fulgerites would depend greatly on temperature. I'm not sure what kind of fused silica you're thinking of using, but I'd recommend fine
grained quartz sand. Also, I'd recommend going for high amperage more so than high voltage - a fatter, hotter spark, as opposed to a long skinny cool
spark.
ssdd - 29-7-2008 at 16:41
@ 12AX7 : I know that's on my to-fix list... One of these days when I find the time I plan to scale down the images...
As for more amps I was thinking that could be a problem so I may have to find a higher amperage supply (perhaps a flyback?).
I was thinking of using what is sometimes referred to as "Cab-O-Sil" which seems to be a very very fine powder.
Thanks,
-ssdd
ShadowWarrior4444 - 29-7-2008 at 16:54
There is a typo on your website, you indicated that the capacitors were 3300 uF, when they are in fact 3300 pF.
As for the fused silica, the discharge from the voltage multiplier will not do much interesting. In order to make a fulgurite you would need much
higher current as previously mentioned--a Marx generator would be able to accomplish it.
An interesting thing to do with the voltage multiplier would be to charge an LC inversion circuit, either to make a TEA laser, or for other
experiments.
vulture - 30-7-2008 at 11:24
Instead of silica I would take silicone glue. This might yield interesting forms of silica when exposed to extreme conditions.
Twospoons - 30-7-2008 at 14:09
When I saw "inch thick layer" and "fused silica" I thought you'll never punch through that with 60kV (thats all you could get with 20x 3kV caps, not
800kV as stated on your website). Then I saw "Cab-o-Sil" which is *fumed* silica - subtle difference.
At any rate, the key point is that you will need a lot of stored energy to get anything interesting to happen. Get one of those monster HV caps off
ebay and you'll be in the right territory. You'll want upwards of 100J stored energy ( just my gut instinct).
[Edited on 31-7-2008 by Twospoons]
ssdd - 30-7-2008 at 16:40
bleh... I'm sorry bout the bad math on that. I rechecked how to calculate the max voltage and I thought it was n_stages * input, but I misread when it
was capacitance * stages. I stand corrected, I pulled down the page until I can correct this.
In the mean time I will be hunting for a massive capacitor which I have wanted one of for some time now.
Thanks for the input,
-ssdd
Twospoons - 30-7-2008 at 17:10
N-stages x input voltage is correct, but with the limitation that the input voltage must be less than half the voltage rating of the individual
capacitors (each cap charges to 2 x V input)
ssdd - 30-7-2008 at 17:29
ahhh OK that makes sense then.
In the meantime I took stock of the capacitors I had laying around. The largest capacitors I have on hand are 75v @ 10000 uF (11.25 joules?). So I
will have to put this project on hold until I can find something with a better energy storage.
-ssdd
** I have also fixed the errors on the page, also I scaled down images to make it less bandwidth intense.
[Edited on 30-7-2008 by ssdd]
DerAlte - 30-7-2008 at 23:12
According to my trusty handbook, the dielectric strength of pure silica is 410 v/mil.
That works out as about half a megavolts, as pointed out above. If, as Twospoons says, nothing 'interesting' would happen unless you discharge 100 J.,
I don't think you would want to do it in a small room. Rent an aircraft hangar.
Half a megavolt is not sciencemadness, its lunacy! With the additional requirement of 100 J, compare it to playing golf in a thunderstorm!
Regards,
Der Alte.
12AX7 - 31-7-2008 at 01:19
Nah, 500kV isn't that much. Pretty typical Van de Graff or Tesla coil territory. Maybe not at 100J, but let's see, that's only 800pF, or a metal
sphere of radius R = C / (4*pi*e_0) = 7.19 m = 23.6' in free space.
According to Wikipedia, one of the largest Van de Graff generators has two conjoined spheres 15' across, which might be roughly half the capacitance.
But they go up to 2MV, which will give double the energy or perhaps 200J.
Tim
Twospoons - 31-7-2008 at 14:34
He'll be able to discharge through powered silica. If it was solid, then it would have to be a huge piece to stop the discharge going around the
edge.
500kV, 100J : sounds like a 10 stage Marx generator with 8nF capacitors charged to 50 kV. Not unreasonable, aside from being insanely dangerous.